It's molasses, Mix your molasses in right before carbonating.
This will give you a thicker head, and a malty flavor. I promise!
If you REALLY want to go out on a limb, Tamari (A type of Soy Sauce) has a strong malty flavor. But it's ultra salty of course, so you would use VERY LITTLE. Of course I've never tried this, just an idea i've had.